1. Field of the Invention
This invention relates to a liquid crystal display apparatus and a method of driving the same. More particularly, this invention relates to a liquid crystal display apparatus provided with a display panel having two-dimensionally arranged pixels, and a method of driving such a display apparatus.
2. Description of the Prior Art
Generally, a conventional active matrix type liquid crystal display (LCD) apparatus has a number of pixels which are arranged in a matrix. FIG. 5 shows the sectional structure of a pixel 20 in a display panel of such an LCD apparatus. In the LCD apparatus shown in FIG. 5, two glass plates 11 and 12 are opposed to each other. On one surface of the glass plate 11, pixel electrodes 13 and signal lines 4 made of indium tin oxide (ITO) are formed, and, on the opposing surface of the other glass plate 12, a common electrode 15 made of ITO is formed. A black matrix 16 is formed on the common electrode 15. Usually, the black matrix 16 is made of a metal such as Cr. Between the two glass plates 11 and 12, a liquid crystal material 17 such as TN (Twisted Nematic) type liquid crystal is filled. Polarizing plates 18 and 19 are disposed on the outer surface of the glass plates 11 and 12, respectively. The liquid crystal disposed between the pixel electrode 13 and common electrode 15 can be simply considered as a light valve switch which is transparent when an adequate voltage is applied and opaque when no voltage is applied. When the LCD apparatus is of the normally black type, a voltage of the same level as that of the common electrode 15 is applied to the pixel electrode 13 of a pixel which is to be displayed as black, through the corresponding signal line 4, thereby making the liquid crystal 17 above the pixel electrode 13 opaque.
In such an active matrix type LCD apparatus of the prior art, when a white level area (area A of FIG. 4) is displayed so that as shown in FIG. 4 it is surrounded by black level areas (areas B-E of FIG. 4), the black level areas B and D which are above and below the white area A in FIG. 4 are not as sufficiently black as the other black level areas C and E. Namely, the gray scale of the black areas B and D has an intermediate value, while signals applied to the pixel electrodes 13 in the areas B and D have a level corresponding to black. This is caused by leakage light or smear (spurious) light due to crosstalk.
This will be described in more detail. When a signal voltage is applied to the pixel electrodes 13 in the area A via the corresponding signal lines 4 which extend in the areas B, A and D, the liquid crystal in the portion E (FIG. 5) which is disposed between the signal lines 4 and the common electrodes 15 also functions as a light valve switch, and becomes transparent. Therefore, light leaks through the liquid crystal in the portion E, resulting in that the gray scale of the areas B and D which should be displayed as black (i.e., the pixel electrodes 13 therein are not energized) becomes to have an intermediate value as a whole.